This invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to insulative magnetic brush toner and developer compositions. In embodiments, the present invention is directed to negatively charged toner compositions comprised of polyester resins, especially certain crosslinked extruded polyesters, wax, optional compatibilizer, pigment, and surface additives of, for example, metal salts of fatty acids, silica particles, metal oxides like titanium dioxide, fluoropolymer particles, such as KYNAR.RTM., and the like, and wherein the developer is comprised of toner and a carrier coated with a polymer, such as polymethylmethylacrylate or mixture of polymers and carbon black.
The developers of the present invention can be preferably selected for insulative magnetic brush imaging systems, and those imaging methods as illustrated in U.S. Pat. Nos. 4,397,264 and 4,948,686, the disclosures of which are totally incorporated herein by reference. Insulative development is particularly appropriate for copying fine-line and/or light density images, such as kanji characters handwritten with a pencil. Insulative development can also generate developed images with an extended tonal range, that is a range of image densities from light gray to black, and this allows, for example, continuous tone images to be copied from input images such as photographs. The extended tonal range characteristic of insulative development is also of utility in digital copiers or printers based on imaging by intensity-modulated lasers.
With the developers of the present invention, low melting polyesters can be selected as the toner resin permitting, for example, lower fuser energies; and the toner size is, for example, from about 7 to about 15 and preferably 9 microns in average volume diameter as determined by a Coulter Counter and narrow GSD in embodiments, for example about 1.3. Additionally, the developers of the present invention in embodiments enable high levels of toner flow, for example from about 7 to about 10 grams per minute, and a developer tribo of from about -10 to about -25 microcoulombs per gram. Moreover, in embodiments the surface additive of a fatty acid salt like zinc stearate or a fluoropolymer, such as KYNAR.RTM., function primarily as a photoreceptor cleaning component and the fumed silica functions primarily as a flow aid, toner blocking avoidance component, and for assistance in achieving excellent admix characteristics. The third additive in the surface mixture assists in achieving a combination of excellent toner flow, admix, and blocking characteristics, and moreover the three surface mixture assists in controlling the tribocharge of the toner, especially with 0.6 weight percent of titanium dioxide P25.RTM. available from Degussa Chemicals, and 0.6 weight percent of the fumed silica TS530.RTM. available from Cabot Corporation, and zinc stearate present in an amount of 0.3 weight percent.
Toner and developers with toner additives like wax and surface additives of, for example, metal oxides, and colloidal slicas are known. Toners with polyesters, including extruded polyesters are also known, reference U.S. Pat. No. 5,227,460, the disclosure of which is totally incorporated herein by reference. In U.S. Pat. No. 4,795,689, there is disclosed an electrostatic image developing toner comprising as essential constituents a nonlinear polymer, a low melting polymer, which is incompatible with the nonlinear polymer, a copolymer composed of a segment polymer, which is at least compatible with the nonlinear polymer, and a segment polymer, which is at least compatible with the low melting polymer, and a coloring agent, see the Abstract, and columns 3 to 10 for example; and U.S. Pat. No. 4,557,991 discloses a toner for the development of electrostatic images comprised of a certain binder resin, and a wax comprising a polyolefin, see the Abstract; also see columns 5 and 6 of this patent and note the disclosure that the modified component shows an affinity to the binder and is high in compatibility with the binder, column 6, line 25.
Developer and toner compositions with certain waxes therein, which waxes can be selected as a component for the toners of the present invention, are known. For example, there are illustrated in U.K. Patent Publication 1,442,835, the disclosure of which is totally incorporated herein by reference, toner compositions containing resin particles, and polyalkylene compounds, such as polyethylene and polypropylene of a molecular weight of from about 1,500 to about 20,000, reference page 3, lines 97 to 119, which compositions prevent toner offsetting in electrostatic imaging processes. Additionally, the '835 publication discloses the addition of paraffin waxes together with, or without a metal salt of a fatty acid, reference page 2, lines 55 to 58. Also, in U.S. Pat. No. 4,997,739, there is illustrated a toner formulation including polypropylene wax (M.sub.w : from about 200 to about 6,000) to improve hot offset. In addition, many patents disclose the use of metal salts of fatty acids for incorporation into toner compositions, such as U.S. Pat. No. 3,655,374. Also, it is known that the aforementioned toner compositions with metal salts of fatty acids can be selected for electrostatic imaging methods wherein blade cleaning of the photoreceptor is accomplished, reference U.S. Pat. No. 3,635,704, the disclosure of which is totally incorporated herein by reference. Additionally, there are illustrated in U.S. Pat. No. 3,983,045 three component developer compositions comprising toner particles, a friction reducing material, and a finely divided nonsmearable abrasive material, reference column 4, beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted, fatty acids preferably of from 8 to 35 carbon atoms, or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43.
Described in U.S. Pat. No. 4,367,275 are methods of preventing offsetting of electrostatic images of the toner composition to the fuser roll, which toner subsequently offsets to supporting substrates, such as papers, wherein there is selected toner compositions containing specific external lubricants including various waxes, see column 5, lines 32 to 45.
However, there are various problems observed with the inclusion of polyolefin or other waxes in toners. For example, when a polypropylene wax is included in toner to enhance the release of toner from a hot fuser roll, or to improve the lubrication of fixed toner image it has been observed that the wax does not disperse well in the toner resin. As a result, free wax particles are released during the pulverizing step in, for example, a fluid energy mill and the pulverization rate is lower. The poor dispersion of wax in the toner resin and, therefore, the loss of wax will then impair the release function it is designed for. Scratch marks, for example, on xerographic developed toner solid areas caused by stripper fingers were observed as a result of the poor release. Furthermore, the free wax remaining in the developer will build up on the detone roll present in the xerographic apparatus causing a hardware failure.
All the problems mentioned above, and others can be eliminated, or minimized with the toner compositions and processes of the present invention in embodiments thereof. The release of wax particles is, for example, a result of, for example, poor wax dispersion during the toner mechanical blending step. The wax additives should be dispersed well in the primary toner resin for them to impart their specific functions to the toner and thus the developer. For some of the additives, such as waxes like polypropylene, VISCOL 550.TM., that become a separate molten phase during melt mixing, the difference in viscosity between the wax and the resin can be orders of magnitude apart, thus causing difficulty in reducing the wax phase domain size. A more fundamental reason for poor dispersion is due to the inherent thermodynamic incompatibility between polymers. The FIory-Huggins interaction parameter between the resin and the wax is usually positive (repulsive) and large so that the interfacial energy remains very large in favor of phase separation into large domains to reduce interfacial area. Some degree of success has been obtained by mechanical blending of the toner formulation in certain types of mixers, such as the known Banbury mixer, where the temperature of melt can be maintained at a low level and polymer viscosities are not that far apart. However, it has been found difficult to generate an effective wax dispersion in compounding extruders where melt temperatures are typically higher. The inclusion of an optional compatibilizer of the present invention is designed to overcome the inherent incompatibility between different polymers, and, more specifically, between toner resin and wax, thus widening the processing temperature latitude and enabling the toner preparation in a large variety of equipment, for example an extruder. The improvement in thermodynamic compatibility will also provide for a more stable dispersion of secondary polymer phase, such as wax, in the host resin against gross phase separation over time.
Illustrated in copending patent applications U.S. Ser. No. 379,822, filed concurrently herewith, is a developer composition comprised of negatively charged toner particles comprised of crosslinked polyester resin particles, pigment particles, and a surface additive mixture comprised of metal salts of fatty acids in an amount of from about 0.2 to about 0.5 weight percent, and silica particles in an amount of from about 0.2 to about 0.5 weight percent; and carrier particles comprised of a core with a coating thereover containing a conductive component; U.S. Ser. No. 379,821, filed concurrently herewith, illustrates a developer composition comprised of a negatively charged toner composition comprised of crosslinked polyester resin particles, pigment particles, wax component particles, a compatibilizer and a surface additive mixture comprised of metal salts of fatty acids, silica particles and metal oxide particles; and carrier particles comprised of a core with a polymer coating or mixture of polymer coatings; and wherein said coating or coatings contain a conductive component; and U.S. Ser. No. 379,838, filed concurrently herewith, illustrates a developer composition comprised of negatively charged toner particles comprised of crosslinked polyester resin particles, pigment particles, and a surface additive mixture comprised of metal salts of fatty acids in an amount of from about 0.2 to about 0.5 weight percent, metal oxide particles in an amount of from about 0.3 to about 1 weight percent, and silica particles in an amount of from about 0.2 to about 0.5 weight percent; and carrier particles comprised of a core with a coating thereover containing a conductive component.